1. Technical Field of the Invention
The present invention relates to reversibly variable electrochromic devices for varying the transmittance to light, such as electrochromic rearview mirrors, windows and sun roofs for motor vehicles, reversibly variable electrochromic elements therefor and processes for making such devices and elements.
2. Brief Description of the Related Technology
Reversibly variable electrochromic devices are known in the art. In such devices, the intensity of light (e.g., visible, infrared, ultraviolet or other distinct or overlapping electromagnetic radiation) is modulated by passing the light through an electrochromic medium. The electrochromic medium is disposed between two conductive electrodes, at least one of which is typically transparent, which causes the medium to undergo reversible electrochemical reactions when potential differences are applied across the two electrodes. Some examples of these prior art devices are described in U.S. Pat. No. 3,280,701 (Donnelly); U.S. Pat. No. 3,451,741 (Manos); U.S. Pat. No. 3,806,229 (Schoot); U.S. Pat. No. 4,712,879 (Lynam) (xe2x80x9cLynam I); U.S. Pat. No. 4,902,108 (Byker) (xe2x80x9cByker Ixe2x80x9d); and I. F. Chang, xe2x80x9cElectrochromic and Electrochemichromic Materials and Phenomenaxe2x80x9d, in Nonemissive Electrooptic Displays, 155-96, A. R. Kmetz and F. K. von Willisen, eds., Plenum Press, New York (1976).
Reversibly variable electrochromic media include those wherein the electrochemical reaction takes place in a solid film or occurs entirely in a liquid solution. See e.g., Chang.
Numerous devices using an electrochromic medium, wherein the electrochemical reaction takes place entirely in a solution, are known in the art. Some examples are described in U.S. Pat. No. 3,453,038 (Kissa); U.S. Pat. No. 5,128,799 (Byker) (xe2x80x9cByker IIxe2x80x9d); Donnely; Manos: Schoot: Byker I; and commonly assigned U.S. Pat. No. 5,073,012 (Lynam) (xe2x80x9cLynam IIxe2x80x9d); U.S. Pat. No. 5,115,346 (Lyman) (xe2x80x9cLyman IIIxe2x80x9d); U.S. Pat. No. 5,140,455 (Varaprasad) (xe2x80x9cVaraprasad Ixe2x80x9d); U.S. Pat. No. 5,142,407 (Varaprasad) (xe2x80x9cVaraprasad IIxe2x80x9d); U.S. Pat. No. 5,151,816 (Varaprasad) (xe2x80x9cVaraprasad IIIxe2x80x9d) and U.S. Pat. No. 5,239,405 (Varaprasad) (xe2x80x9cVaraprasad IVxe2x80x9d); and commonly assigned co-pending U.S. patent application Ser. No. 07/935,784 filed Aug. 27, 1992) now U.S. Pat. No. 5,500,760. Typically, these electrochromic devices, sometimes referred to as electrochemichromic devices, are single-compartment, self-erasing, solution-phase electrochromic devices. See e.g., Manos, Byker I and Byker II.
In single-compartment, self-erasing, solution-phase electrochromic devices, the intensity of the electromagnetic radiation is modulated by passing through a solution held in a compartment. The solution often includes a solvent, at least one anodic compound and at least one cathodic compound. During operation of such devices, the solution is fluid, although it may be gelled or made highly viscous with a thickening agent, and the solution components, including the anodic compounds and cathodic compounds, do not precipitate. See e.g., Byker I and Byker II.
Certain of these electrochemichromic devices have presented drawbacks. First, a susceptibility exists for distinct bands of color to form adjacent the bus bars after having retained a colored state over a prolonged period of time. This undesirable event is known as segregation. Second, processing and manufacturing limitations are presented with electrochemichromic devices containing electrochemichromic solutions. For instance, in the case of electrochemichromic devices which contain an electrochemichromic solution within a compartment or cavity thereof, the size and shape of the electrochemichromic device is limited by the bulges and non-uniformities which often form in such large area electrochemichromic devices because of the hydrostatic nature of the liquid solution. Third, from a safety standpoint, in the event an electrochemichromic device should break or become damaged through fracture or rupture, it is important for the device to maintain its integrity so that, if the substrates of the device are shattered, an electrochemichromic solution does not escape therefrom and that shards of glass and the like are retained and do not scatter about. In the known electrochromic devices, measures to reduce breakage or broken glass scattering include the use of tempered glass and/or a laminate assembly comprising at least two panels affixed to one another by an adhesive. Such measures control the scattering of glass shards in the event of breakage or damage due, for instance, to the impact caused by an accident.
Numerous devices using an electrochromic medium, wherein the electrochemical reaction takes place in a solid layer, are known in the art. Typically, these devices employ electrochromic solid-state thin film technology [see e.g., N. R. Lynam, xe2x80x9cElectrochromic Automotive Day/Night Mirrorsxe2x80x9d, SAE Technical Paper Series, 870636 (1987); N. R. Lynam, xe2x80x9cSmart Windows for Automobilesxe2x80x9d, SAE Technical Paper Series, 900419 (1990); N. R. Lynam and A. Agrawal, xe2x80x9cAutomotive Applications of Chromogenic Materialsxe2x80x9d, Large Area Chromogenics: Materials and Devices for Transmittance Control, C. M. Lampert and C. G. Granquist, eds., Optical Eng""g Press, Washington (1990); C. M. Lampert, xe2x80x9cElectrochromic Devices and Devices for Energy Efficient Windowsxe2x80x9d, Solar Energy Materials, 11, 1-27 (1984); U.S. Pat. No. 3,521,941 (Deb); U.S. Pat. No. 4,174,152 (Giglia); Re. 30,835 (Giglia); U.S. Pat. No. 4,338,000 (Kamimori); U.S. Pat. No. 4,652,090 (Uchikawa); U.S. Pat. No. 4,671,619 (Kamimori); Lynam I; and commonly assigned U.S. Pat. No. 5,066,112 (Lynam) (xe2x80x9cLynam IVxe2x80x9d) and U.S. Pat. No. 5,076,674 (Lynam) (xe2x80x9cLynam Vxe2x80x9d)].
In solid-state thin film electrochromic devices, an anodic electrochromic layer and a cathodic electrochromic layer, each layer usually made from inorganic metal oxides, are typically separate and distinct from one another and assembled in a spaced-apart relationship. The solid-state thin films are often formed using techniques such as chemical vapor deposition or physical vapor deposition. Such techniques are not attractive economically, however, as they involve cost. In another type of solid-state thin film electrochromic device, two substrates are coated separately with compositions of photo- or thermo-setting monomers or oligomers to form on one of the substrates an electrochromic layer, with the electrochromic material present within the layer being predominantly an inorganic material, and on the other substrate a redox layer. [See Japanese Patent Document JP 63-262,624].
Attempts have been made to prepare electrochromic media from polymers. For example, it has been reported that electrochromic polymer layers may be prepared by dissolving in a solvent organic polymers, which contain no functionality capable of further polymerization, together with an electrochromic compound, and thereafter casting or coating the resulting solution onto an electrode. It has been reported further that electrochromic polymer layers are created upon evaporation of the solvent by pressure reduction and/or temperature elevation. [See e.g., U.S. Pat. No. 3,652,149 (Rogers), U.S. Pat. No. 3,774,988 (Rogers) and U.S. Pat. No. 3,873,185 (Rogers); U.S. Pat. No. 4,550,982 (Hirai); Japanese Patent Document JP 52-10,745; and Y. Hirai and C. Tani, xe2x80x9cElectrochromism for Organic Materials in Polymeric All-Solid State Systemsxe2x80x9d, Appl. Phys. Lett., 43(7), 704-05 (1983)]. Use of such polymer solution casting systems has disadvantages, however, including the need to evaporate the solvent prior to assembling devices to form polymer electrochromic layers. This additional processing step adds to the cost of manufacture through increased capital expenditures and energy requirements, involves potential exposure to hazardous chemical vapors and constrains the type of device to be manufactured.
A thermally cured polymer gel film containing a single organic electrochromic compound has also been reported for use in display devices. [See H. Tsutsumi et al., xe2x80x9cPolymer Gel Films with Simple Organic Electrochromics for Single-Film Electrochromic Devicesxe2x80x9d, J. Polym. Sci., 30, 1725-29 (1992) and H. Tsutsumi et al., xe2x80x9cSingle Polymer Gel Film Electrochromic Devicexe2x80x9d, Electrochemica Acta, 37, 369-70 (1992)]. The gel film reported therein was said to possess a solvent-like environment around the electrochromic compounds of that film. This gel film was reported to turn brown, and ceased to perform color-bleach cycles, after only 35,200 color-bleach cycles.
The present invention provides electrochromic polymeric solid films (xe2x80x9cpolychromic solid filmsxe2x80x9d) that are prepared by an in situ curing process different from processes used to prepare the electrochromic polymer layers known to date, and employ different combinations of electrochromic compounds than those that have been placed heretofore in solid electrochromic media. The resulting polychromic solid films possess beneficial properties and characteristics, and offer superior results, compared to the known electrochromic media. For instance, polychromic solid films overcome well-known manufacturing and use concerns such as hydrostatic pressure that is particularly troublesome in large area vertically mounted panels, such as windows, or large area mirrors, such as Class 8 truck mirrors. Thus, polychromic solid films are extremely well-suited to commercial applications, like the manufacture and use of electrochromic devices. Such electrochromic devices include, but are not limited to, electrochromic mirrorsxe2x80x94e.g., vehicular, for instance, truck mirrors, particularly large area truck mirrors, automotive interior and exterior mirrors, architectural or specialty mirrors, like those useful in periscopic or dental and medical applications; electrochromic glazingsxe2x80x94e.g., architectural, such as those useful in the home, office or other edifice, aeronautical, such as those useful in aircraft, or vehicular glazings, for instance, windows, such as windshields, side windows and backlights, sun roofs, sun visors or shade bands and optically attenuating contrast filters, such as contrast enhancement filters, suitable for use in connection with cathode ray tube monitors and the like; electrochromic privacy or security partitions; electrochromic solar panels, such as sky lights; electrochromic information displays; electrochromic lenses and eye glass. Moreover, in view of the teaching herein, any of such electrochromic devices may be manufactured to be segmented so that a portion of the device colors preferentially to change the light transmittance thereof.
The present invention also provides novel electrochromic monomer compositions comprising anodic electrochromic compounds, cathodic electrochromic compounds, a monomer component and a plasticizer that are useful in the formation of such polychromic solid films. More specifically, each of the electrochromic compounds are organic or organometallic compounds. Electrochromic monomer compositions may also include, but are not limited to, either individually or in combination, cross-linking agents, photoinitiators, photosensitizers, ultraviolet stabilizing agents, electrolytic materials, coloring agents, spacers, anti-oxidizing agents, flame retarding agents, heat stabilizing agents, compatibilizing agents, adhesion promoting agents, coupling agents, humectants and lubricating agents.
The present invention further provides novel processes for making polychromic solid films by transforming such novel electrochromic monomer compositions into polychromic solid films through exposure to electromagnetic radiation for a time sufficient to effect an in situ cure.
The present invention still further provides electrochromic devices, such as those referred to above, particularly rearview mirrors, windows and sun roofs for automobiles, which devices are stable to outdoor weathering, particularly weathering observed due to prolonged exposure to ultraviolet radiation from the sun, and are safety protected against impact from an accident. Such outdoor weathering and safety benefits are achieved by manufacturing these devices using as a medium of varying transmittance to light the polychromic solid films prepared by the in situ cure of an electrochromic monomer composition containing a monomer component that is capable of further polymerization.
The present invention provides for the first time, among other things (1) polychromic solid films that may be transformed from electrochromic monomer compositions by an in situ curing process through exposure to electromagnetic radiation, such as ultraviolet radiation; (2) a transformation during the in situ curing process from the low viscosity, typically liquid, electrochromic monomer compositions to polychromic solid films that occurs with minimum shrinkage and with good adhesion to the contacting surfaces; (3) polychromic solid films that (a) may be manufactured to be self-supporting and subsequently laminated between conductive substrates, (b) perform well under prolonged coloration, (c) demonstrate a resistance to degradation caused by environmental conditions, such as outdoor weathering and all-climate exposure, particularly demonstrating ultraviolet stability when exposed to the sun, and (d) demonstrate a broad spectrum of color under an applied potential; (4) polychromic solid films that may be manufactured economically and are amenable to commercial processing; (5) polychromic solid films that provide inherent safety protection not known to electrochromic media heretofore; and (6) electrochromic monomer compositions that comprise anodic electrochromic compounds and cathodic electrochromic compounds, which compounds are organic or organometallic.
The self-supporting nature of polychromic solid films provides many benefits to the electrochromic devices manufactured therewith, including the elimination of a compartmentalization means, such as a sealing means, since no such means is required to confine or contain a polychromic solid film within an electrochromic device. That polychromic solid films may be manufactured to be self-supporting also enhances processibility, and vitiates obstacles well-recognized in the manufacturing of electrochromic devices containing known electrochromic media, especially those that are to be vertically mounted in their intended use.
Moreover, since the electrochromic compounds are not free to migrate within polychromic solid films, in contrast to electrochromic compounds present within a liquid solution-phase environment, polychromic solid films do not pose the segregation concern as do solution-phase electrochemichromic devices; rather, polychromic solid films perform well under prolonged coloration.
Further, from a safety perspective, in the event that electrochromic devices manufactured with polychromic solid films should break or become damaged due to the impact from an accident, no liquid is present to seep therefrom since the polychromic solid films of the present invention are indeed solid. Also, the need to manufacture electrochromic devices with tempered glass, or with at least one of the substrates being of a laminate assembly, to reduce potential lacerative injuries is obviated since polychromic solid films, positioned between, and in abutting relationship with, the conductive surface of the two substrates, exhibit good adhesion to the contacting surfaces. Thus, polychromic solid films should retain any glass shards that may be created and prevent them from scattering. Therefore, a safety protection feature inherent to polychromic solid films is also provided herein, making polychromic solid films particularly attractive for use in connection with electrochromic devices, such as mirrors, windows, sun roofs, shade bands, eye glass and the like.
Polychromic solid films embody a novel and useful technology within the electrochromic art, whose utility will become more readily apparent and more greatly appreciated by those of skill in the art through a study of the detailed description taken in conjunction with the figures which follow hereinafter.